1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device having a thin-film resistor.
2. Related Arts
Various thin-film resistors made of a CrSi compound or the like integrated on an IC are hitherto proposed. For example, as shown in EP-A-0350961 or EP-A-0443575, such thin-film resistor is formed as follows: a layer insulating film is formed on a substrate with a semiconductor element; a thin-film material such as CrSi compound or the like is deposited; after patterning the thin-film material into the thin-film resistor, a contact hole is formed on the layer insulating film; and a wiring electrode made of aluminum or the like is formed.
That is, a thin-film resistor is constituted and thereafter a contact hole is formed. This is because of the following reason. Although two types of methods such as wet etching and dry etching are considered as methods for patterning a CrSi film, the dry etching method is more prospective because wet etching has a problem that fluctuation of etching of the CrSi film increases. In the case of normal dry etching using plasma, however, if a contact hole opens in an element area when patterning a thin-film resistor, the semiconductor exposed area is damaged. Specifically, a problem occurs that plasma under dry etching collides with the element area exposed in the contact hole to cause an element defect and an imperfect contact with an electrode, i.e., an open circuit. Therefore, a contact hole should be formed after a thin-film resistor is patterned.
However, when forming a contact hole after CrSi patterning, it is clarified that the following problem occurs. That is, when forming a contact hole after depositing and patterning a CrSi thin-film resistor, as shown in FIG. 5A (in this figure, CrSi thin-film resistor is not shown), photoresist 8 is formed on a layer insulating film 2 to use it as an etching mask. In this case, the adhesiveness of the photoresist 8 is deteriorated because surface chapping occurs under etching of CrSiN film performed in the preceding process and thereby, the photoresist 8 is lifted due to peeling. Therefore, when forming a contact hole through wet etching, the layer insulting film 2 is excessively etched, and the contact hole expands to expose the p-n junction formed on the semiconductor substrate 1 as shown in FIG. 5B.